New Bipedal Lizard Sighting From Utah

I have recently been informed of a new bipedal lizard sighting. It happened in Arches National Park near Moab, Utah in the Summer of 2011. A man saw several bipedal lizards in a pack. They were about 4 feet tall. He then drew a sketch of the animal that he had seen. It was lightly-built, with long legs and a long neck.

Here is the sketch:

Using this sketch and the information from this sighting, I have been able to come up with a new hypothesis about these lizards. I have modified the ideas that I previously had about them.

I now think that they are closely-related to the Collared Lizard. They are around 4 feet tall, 10 feet long, and weighing around 32 pounds (possibly up to 40 pounds or so in the largest specimens). They are lightly-built, with long legs, a long neck, and a long tail. They are capable of running very quickly on their hind legs.

They are vicious predators who hunt in packs, and there are stories of them killing humans. Both the predatory behavior and the pack-hunting behavior leads me to believe that these lizards might possibly be related to the Collared Lizard, which also lives in the Southwestern United States. Collared Lizards are also vicious predators, and they have also been observed using pack-hunting tactics to flush out their prey.
This lizard would pretty much be a gigantic and more strongly-bipedal version of the Collared Lizard.

This is probably the best sighting report I have ever heard of. I am looking forward to receiving more sighting reports of these fascinating animals in the near future.